Cannot send or receive faxes with external fax machine

Although you configured the fax device according to our guide and can conduct calls over the FRITZ!Box, you cannot send or receive faces. Faxes cannot be transmitted or transmission is aborted. One of the following error messages may be displayed in the event log of the FRITZ!Box:

"Not Acceptable Here (488)"

"Unsupported Media Type (415)"

"Not Acceptable Here (606)"

Important:Some of the settings described here are only displayed if the advanced view is enabled in the user interface. The configuration procedure and notes on functions given in this guide refer to the latest FRITZ!OS.

Simply proceed as described below. After each measure, check whether the issue persists.

2 Checking the event log of the FRITZ!Box

Check whether one of the following error messages is displayed for a failed fax. If this is the case, note the information that correspond to the message.

If the message "Unsupported Media Type (415) is displayed, then your provider does not support the requested codec or generally does not allow fax transmission.

If the message "Not Acceptable Here (488 or 606)" is displayed, then your provider does not support the T.38 standard. Without T.38 (Fax over IP), fax transmission over the Internet is not reliable.

3 Enabling the fax switch (passive)

If you would like to use your analog landline number to receive telephone calls as well as faxes, enable the FRITZ!Box's fax switch. The fax switch automatically forwards faxes to a fax machine configured in the FRITZ!Box:

Important:In order for faxes to be recognized and forwarded, a different device, for example a telephone or answering machine, must accept the call first. The fax switch does not recognize calls that are not accepted.

Look for aborted faxes under "Display table on completed telephone calls" and check whether "T.38" is displayed in the "Coding" column for these faxes:

If "T.38" is displayed, then T.38 was used for the fax transmission.

If "T.38" is not displayed, then T.38 was not used. Without T.38 (Fax over IP), fax transmission over the Internet is not reliable.

Note:If your Internet telephony provider does not support T.38, then you can use an Internet number of an Internet telephony provider that does support T.38 to receive faxes. If your FRITZ!Box is connected with an analog landline, you can also use your landline number instead of the Internet number for faxing.

If you are still not able to send or receive a fax using a landline number, or it is aborted, there are unfortunately no further settings in your FRITZ!Box that influence faxing. In such cases, the problem lies with the fax.

Note:Often, the manufacturer of a fax machine can give you helpful advice on how to ideally configure the fax machine for use with a PBX.